[Python-Dev] About dictionary lookup caching

[Brett Cannon]

On 12/19/06, Andrea Griffini <agriff at tin.it> wrote:
>
> I'm experimenting with a patch for dictionary lookup caching, the
> main idea being avoiding the lookup of a constant (co_names) in
> a dictionary if the dictionary didn't change since last lookup.
>
> Currently the cache is held in a structure that is parallel to
> co_names (the LOAD_GLOBAL opcode uses oparg to access
> the cache slot) and this is wasteful if there are co_names entries
> that are not used for global lookups.
>
> Probably I could act at the code object creation time to
> sort names so that ones used by LOAD_GLOBAL are
> at the beginning of co_names but this would require inspecting
> and hacking the already generated opcode.
> Another case that would IMO be worth optimizing is the
> LOAD_ATTR lookup when it's done after a LOAD_GLOBAL
> (I suspect that in many cases the element being searched will
> be a module so caching would be simple to implement; for
> general objects things are way more complex and I see no
> simple solution for caching dictionary lookups).
>
> My opinion is that it would be by far better to do this ordering
> of co_names at compile time but I've no idea where to look
> for trying to make such a change.
>
> Can someone please point me in the right direction ?


For guidance on how the compiler works, see PEP 339 (
http://www.python.org/dev/peps/pep-0339).

-Brett
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